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Title: Mechanisms of degradation in adhesive joint strength: Glassy polymer thermoset bond in a humid environment

The degradation in the strength of napkin-ring (NR) joints bonded with an epoxy thermoset is evaluated in a humid environment. While adherend composition (stainless steel and aluminum) and surface preparation (polished, grit blasted, primed, coupling agent coated) do not affect virgin (time=0) joint strength, they can significantly affect the role of moisture on the strength of the joint. Adherend surface abrasion and corrosion processes are found to be key factors in determining the reliability of joint strength in humid environments. In cases where surface specific joint strength degradation processes are not active, decreases in joint strength can be accounted for by the glass transition temperature, Tg, depression of the adhesive associated with water sorption. Under these conditions, joint strength can be rejuvenated to virgin strength by drying. In addition, the decrease in joint strength associated with water sorption can be predicted by the Simplified Potential Energy Clock (SPEC) model by shifting the adhesive reference temperature, Tref, by the same amount as the Tg depression. When surface specific degradation mechanisms are active, they can reduce joint strength below that associated with adhesive Tg depression, and joint strength is not recoverable by drying. Furthermore, a critical relative humidity (or, potentially, critical watermore » sorption concentration), below which the surface specific degradation does not occur, appears to exist for the polished stainless steel joints.« less
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  1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 0143-7496; 533734
Grant/Contract Number:
Accepted Manuscript
Journal Name:
International Journal of Adhesion and Adhesives
Additional Journal Information:
Journal Volume: 63; Journal Issue: C; Journal ID: ISSN 0143-7496
Research Org:
Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org:
Country of Publication:
United States
36 MATERIALS SCIENCE adhesion; degradation; humidity; mechanism; viscoelasticity